COROT and the Hunt for Rocky Worlds

by Paul Gilster on October 27, 2006

The COROT mission, to be launched in December, promises to move us to the next level of planetary detection. Devoted to studying exoplanet transits, in which a planet crosses the face of its star as seen from Earth, the space telescope will probably detect numerous ‘hot Jupiters.’ But an even more interesting possibility is rocky worlds in close orbit around their stars. And the thinking is that planets only a few times larger than Earth — and perhaps even smaller than that — will be within its reach.

Any star with a transiting planet will provide a telltale drop in light that, depending on the size of the planet and the distance of the star, may be measurable. But COROT (the acronym stands for Convection Rotation and planetary Transits) is most sensitive to rocky worlds in orbits of 50 days or less. If that sounds dismaying in terms of habitability, consider that a planet in such an orbit around a dim red dwarf could be located ideally within the star’s habitable zone. And red dwarfs comprise on the order of 70 percent of the stars in the Milky Way (excluding brown dwarfs).

Also under study is the intriguing field of asteroseismology. As sound waves ripple across a star’s surface, they produce variations in its light that help us understand the internal conditions of the star. Asteroseismology sounds exotic, but it’s already well established in the study of our own Sun. The Solar and Heliospheric Observatory (SOHO) has fine-tuned the method. Now COROT will target at least fifty stars for specific study in its examination of stellar evolution.

Launch is scheduled for the end of the year at the Soyuz-Fregat launcher at Baikonur, Kazakhstan. As we get COROT into space and anticipate the Kepler launch in October of 2008, it’s heartening to consider how far we’ve come. The earliest planetary detections were short period worlds; i.e., planets that completed their orbits in mere days. They’re easier to detect because they produce the strongest data signature, but long-period planets are a much harder catch.

Nonetheless, teams have been observing numerous stars in an attempt to build up enough data to detect such worlds, and the results are beginning to come in. That has opened up the study of multiple planets in systems already known to have one, and it begins to flesh out our picture of how planetary systems diverge. Moving into the era of small, rocky worlds has big implications as we hunt out possible havens for life. The bet here is that red dwarfs are going to prove fertile hunting grounds for planets of the right distance, size and composition. But finding an Earth-sized world around a Sun-like star remains the ultimate prize.

There’s no end to what imagination can dignify with a fine draping in possibilities.

How about: after 13 billion years of existence, the primary habitat for intelligence in the universe is inside hollowed out brown dwarfs which — any second now — our instruments will be able to “see” and may find that they’re as numerous and as diversely commanded as yachts in Miami, and just as full of party-time sentients — only in this case, each dwarf will harbor billions of them from a million cultures borne across the eons.

Be some introduction to the universe for us, eh? Be like the lights were turned on suddenly and one finds oneself in the middle of an orgy — of information.

Mostly, we face invisible thresholds now. They’re like black holes — might not see them until they see you!

There are a few papers out there which suggest planets such as Gliese 876 d and the “hot Neptunes” around other red dwarfs could be gigantic ocean planets with a liquid water layer above an ice mantle and silicate core. Whether a high-gravity, high-temperature ocean world qualifies as “habitable” is another matter.

In addition, current theoretical models have quite a lot of trouble forming Jupiter-mass planets (e.g. the planets around Gliese 876 and Gliese 849) around red dwarfs, so I think ruling out the formation of Earth-mass planets in the HZ of red dwarfs is premature at this stage.

Terran planets in the right place and of the right mass will be rare around red dwarfs – like Jovians – but not totally ruled out of court either. As for “hollowed out” brown dwarfs… can’t happen. Perhaps you mean Dyson shells made from brown dwarf masses?

I vote that the first rocky earthsize world discovered outside our solar system be named “Sparky” after Charles Schultz.

“I got a rock.” said Charlie Brown…

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Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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